[5.7][ConstraintSystem] Use witnesses for makeIterator and next refs in for-in context

[xedin]

Cherry-pick of #61091

---

• Explanation:

Fixes behavior change introduced in 5.7 which goes against the original design of for-in loops
where makeIterator() and next() calls that form a loop statement should use witness of
Sequence#makeIterator and IteratorProtocol#next requirements instead of relying on overload
resolution.

For example:

extension Array where Element == Double {
  func makeIterator() -> Array<Int>.Iterator {
    return [1, 2, 3].makeIterator()
  }
}

for i in [4.0, 5.0, 6.0] {
  print(i)
}

makeIterator declared in the Array extension is not a witness to Sequence#makeIterator
and shouldn't be used because that would change runtime behavior.

• Scope: makeIterator and next calls injected by the compiler in for-in context.

• Main Branch PR: [ConstraintSystem] Use witnesses for makeIterator and next refs in for-in context #61091

• Resolves: Sequence/Iterator conformance broken in 5.7 #60514, [Regression] Ambiguous makeIterator() in 5.7 #60958

• Risk: Low

• Reviewed By: @hborla

• Testing: Added a regression test-case to the suite.

[xedin]

@swift-ci please test

[xedin]

@swift-ci please test

[RLovelett]

I am using the swift version in Xcode 14.0.1 (14A400) (aka the 14.0.1 RC). Is this fix in there?

swift-driver version: 1.62.8 Apple Swift version 5.7 (swiftlang-5.7.0.127.4 clang-1400.0.29.50)
Target: x86_64-apple-macosx12.0